Freeze dryer using an expendable refrigerant

ABSTRACT

A FREEZE DRYING ARRANGEMENT HAVING MEAS TO PERMIT THE USE OF AN EXPENDABLE REFRIGERANT. A TRANSPARENT DOOR IS ALSO DISCLOSED HAVING A METALLIC LAYER THEREON TO PERMIT VIEWING THERETHROUGH WHILE REFLECTING RADIANT ENERGY WHICH COULD AFFECT THE TEMPERATURE LEVEL IN T HE CHAMBER.

Feb. 23, 1971 I s, FRASER v 3,564,727

FREEZE DRYER USING AN EXPENDABLE REFRIGERANT Filed March 5, 1969 Fl c 3INVENTOR DOUGLAS 5. FRASER Q if ZV ZTT'X United States Patent 3,564,727FREEZE DRYER USING AN EXPENDABLE REFRIGERANT Douglas S. Fraser, NewPaltz, N.Y., assignor to The Virtis Company, Inc., Gardiner, N.Y., acorporation of New York Filed Mar. 3, 1969, Ser. No. 803,760 Int. Cl.F26b 13/30 US. C]. 3492 4 Claims ABSTRACT OF THE DISCLOSURE A freezedrying arrangement having means to permit the use of an expendablerefrigerant. A transparent door is also disclosed having a metalliclayer thereon to permit viewing therethrough while reflecting radiantenergy which could affect the temperature level in the chamber.

This invention relates to improvements in freeze drying chambers and,more specifically, to a new and improved refrigeration system adaptedfor use with an expendable refrigerant and a novel reflective door forsaid drying chambers.

In the practice of freeze drying, the material is first frozen and thensubjected to a high vacuum and controlled heat input. Under theseconditions, the frozen water content of the material is removed throughsublimation which, by definition, consists of ice going to vapor,bypassing the intermediary liquid phase. In the accomplishment of freezedrying, vacuum chambers have been utilized which are cylindrical ortubular in shape. They are fabricated with a transparent or clear accessdoor which is properly sealed to be vacuum tight. Within the vacuumchamber is provided a product shelf having means to permit it to beheated under controlled circumstances. Ideally, refrigeration should beprovided to permit the prefreezing of the materials to be dried and thuseliminating the need for a separate freezing chamber. Even if freezingis done elsewhere, refrigeration should be provided to form a condensingsurface to collect the water vapor and prevent it from gaining access tothe vacuum pump which continuously evacuates the vacuum chamber duringthe freeze drying process.

In the past, chambers of this general type have been used with amechanically operated refrigeration system. Because of the size of therefrigeration system required, the complete freeze drying unit, ofnecessity, was fairly sizable. Oftentimes, the space required and thecost of such a unit was beyond the space available and the budget ofsmaller laboratories having only an occasional need for a freeze dryer.

The present invention relates to a freeze dryer of the chamber typewhich may also be included with connections for manifold-type drying aswell as chamber drying. The present design includes a novelrefrigeration system which utilizes an expendable refrigerant locatedoutside the freezing chamber. A novel exchange system of closed circuitdesign is used to transfer the heat from the expendable refrigerant tothe interoir of the vacuum chamber. This system may be also utilized tomaintain the products in a frozen state or freeze dry products whilepositioned on the shelf. The exchange system also acts as a condensingsurface to collect the water vapor during freeze drying. As anadditional feature, the present invention contemplates the use of anovel door which reflects heat energy while permitting viewing of thespecimens in the chamber.

The present system provides a refrigeration unit of good efficiencywhich is considerably less expensive than the mechanical refrigerationunits heretofore known. It

3,564,727 Patented Feb. 23, 1971 does not have the drawbacks ofpreviously used techniques of positioning chunks of Dry Ice inreceptacles adjacent the vacuum chamber.

The refrigeration unit also serves multiple functions, freezing andcondensing out the water vapors. All of the advantages of more expensivesystems are gained without a significant sacrifice in refrigerationefiiciency. Other advantages will be seen upon description of apreferred form of the invention.

It is an object of this invention to provide a new and improved freezedrying chamber having a novel door permitting viewing of the contentswhile reflecting any heat energy which ordinarily would pass throughsaid door.

It is a further object of this invention to provide a new and improvedfreeze drying arrangement having a novel refrigeration system which willbe relatively inexpensive to manufacture and assemble, thereby placingit within the reach of users having only occasional need for freezedrying equipment.

It is a further object of this invention to provide a new and improvedfreeze drying arrangement having a novel refrigeration system whichutilizes an expendable refrigerant.

It is a still further object of this invention to provide a new andimproved refrigeration system for use with freeze drying equipment whichmay be readily manufactured and assembled.

Objects other than those specifically set forth will become apparent tothe person skilled in the art upon reference to the accompanyingdrawings and following description.

In the drawings:

FIG. 1 is a front elevational view of the freeze drying apparatus of thepresent invention;

FIG. 2 is an enlarged cross-sectional view of the upper portion of thefreeze drying chamber shown fragmentarily and the refrigeration systemshown in cross section; and

FIG. 3 is a further enlarged cross-sectional view taken generally alongthe line 33 of FIG 2.

Referring now to FIG. 1, a freeze drying arrangement of the presentinvention is indicated generally by reference character 10. The freezedrying arrangement includes a vacuum chamber 11 and refrigeration system1 2 which is disposed on top of the vacuum chamber '11.

The vacuum chamber 11 consists of a cylindrical drum 13 supported on ahousing 14. The housing 14 may include suitable controls such as atemperature control 15, stoppering control 16 and shelf heat switch 17,all of which function in a known manner.-

The chamber 11 includes a bottom shelf 18 on which is positioned a tray20 having bottles 21 of material to be freeze dried. A stoppering plate22 is located above the bottles 21 and is provided on the underside withan elastomeric diaphragm 23 which, through the use of the stopperingcontrol, expands downwardly to seat stoppers 24 in the mouth of thebottles or containers 21 after freeze drying is completed. This is aconventional or known type of stoppering which is known to the art.

Manifold units in the form of valves 25 may be provided along oppositesides of the vacuum chamber 11. Each valve may be of the type describedin co-pending application Ser. No. 650,134, assigned to the assignee ofthe present invention. The disclosure of that application isincorporated herein by reference. The front of the chamber is closed offby a transparent door 26 of plastic having vacuum metal depositedthereon. This permits the operator to observe the freeze drying processwhile reflecting heat from outside sources and maintaining the heatlevel in the chamber fairly constant. External heat is reflected whilefull viewing of the specimens being dried is available. The totalreflectance should be of the order of about 75%. The chamber 11 isprovided with suitable connections (not shown) for attachment to avacuum pump capable of evacuating the interior of the chamber 11.Ideally, the vacuum connection is lo cated where the fiow of vapor willbe past the condensing surface in the chamber.

The expendable refrigeration unit 12 is of box-like form and disposed onthe top of the vacuum chamber 11. As seen in FIGS. 2 and 3, therefrigeration unit includes a closed tube 30 having heat exchange means31 located centrally of a receptacle 32 which is located within ahousing 33. An insulating foam 34 is formed in the space between thereceptacle 32 and the housing 33, both of which may be rectangular asshown or of any other suitable shape. The closed tube 30 extends withinthe vacuum chamber 12 and communicates with a generally X-shapedcondenser having a plurality of condensing fins 35, 36, 37 and 38 at therespective ends. Obviously, the condenser may be of any desiredconfiguration. The heat exchange surfaces 31, 35, 36, 37 and 38 areformed by a plurality of metallic fins which are joined to the closedtube 30 by suitable means such as soldering, welding or the like toprovide for optimum heat transfer.

The heat exchange means 31 is surrounded in the Well 32 by an expendablerefrigerant 40 which may include Dry Ice chunks 41 immersed in analcohol or acetone bath 42. Inasmuch as the well 32 is well insulatedfrom the outer housing 33 by a layer of foam several inches thick andcovered by a suitable cover 43, the expendable refrigerant will last forapproximately 24 hours.

The tube 30 forms a closed refrigeration circuit and is filled with asuitable refrigerant such as Freon 13 which boils at about 115 F. Gaseswhich would serve as a refrigerant in this system are nitrous oxide,refrigerant 503, ethane ethylene and possibly others. The pressure rangewould vary between about 200 p.s.i. to 700 p.s.i., depending upon therefrigerant.

The refrigeration cycle which occurs is as follows: As the refrigerantis cooled at the upper end of the tube 30 by the expendable refrigerant40, it goes to a liquid state, draining down to the bottom of the tubeand into the condensing area of the heat exchangers 3538. As the heatexchange means in the chamber 12 is warmed through loss of heat duringthe freeze drying or refrigeration of the material to be freeze dried,the refrigerant is heated to above its boiling point and assumes a gasform, rising in the tube 30 to the area of the heat exchange means 31.There the refrigerant is again cooled and the cycle repeats itself.

It is contemplated that the refrigerant will be maintained in the tube30 under a pressure. As indicated, this will vary with the type ofrefrigerant used, however, in the preferred form, when a refrigerantknown as Freon 13 is utilized, it is under a pressure of the order of300 It can be appreciated from consideration of the foregoing embodimentthat the freeze drying system of the present invention is complete withthe exception of a suitable vacuum source. Because of its simplifiedconstruction, it may be produced economically to place it within theeconomic range of small laboratories. With the refrigeration systemshown, it may be used as a freezer to freeze the materials to be driedand thereafter used as a @ondenser u g the freeze drying process.Because of the novel construction of the refrigeration system, it willoperate etficiently and utilize a minimum of Dry Ice. Heat istransferred in the present invention by latent heat of liquid used,permitting large amounts of heat to be transferred through a relativelysmall tube which, in one embodiment, had an outside diameter offive-eighths /8) inch. The location of the condenser permits thetemperature to be maintained until the last fragment of Dry Ice has beenexpended. The reflective door prevents heat loss or gain by radiantheating exterior of the chamber while permitting a full view of thechamber contents during drying.

' Upon a consideration of the foregoing, it will become obvious to thoseskilled in the art that various modifications may be made withoutdeparting from the invention embodied herein. Therefore, only suchlimitations should be imposed as are indicated by the spirit and scopeof the appended claims.

Iclaim:

1. A freeze drying unit comprising a closed vacuum chamber adapted to beevacuated, condensing and refrigeration means for cooling said chamberand condensing vapors during freeze drying, said refrigeration andcondensing means including a housing for a receptacle, said receptaclebeing located adjacent said vacuum chamber and adapted to receive anexpendable refrigerant, a closed tube forming a refrigeration transfermedium, said closed tube extending from said receptacle into said vacuumchamber, a first heat exchange means formed on said closed tube withinsaid chamber, a second heat exchange means on said tube in saidreceptacle and adapted for directly contacting said expendablerefrigerant and a pressurized gas in said closed tube to maintain saidfirst heat exchange means in said chamber at a temperature below thetemperature required to condense the vapor out of the materials beingdried.

2. The freeze drying unit of claim 1 wherein said refrigerant in saidclosed tube is under a pressure in the range from about 200 pounds persquare inch to about 700 pounds per square inch.

3. In a chamber-type freeze dryer having a door thereon to gain accessto said chamber, while maintaining said chamber vacuum-tight, theimprovement comprising said door having a metallic substance thereon toreflect heat energy on both sides thereof while permitting viewingtherethrough.

4. The improvement in chamber-type freeze dryers as defined in claim 3wherein said door is about reflective.

References Cited UNITED STATES PATENTS 1,176,313 3/1916 Pfund 1l733.31,975,868 10/1934 Schlumbolun 62-333 2,097,685 11/1937 Botton 62--3332,437,332 3/1948 Newton 62-332 2,564,708 8/1951 Mochel 11733.3 2,907,11710/1959 Parkinson 34-92 3,242,575 3/1966 Moudresi 34-92 3,264,747 8/1966 Fuentevilla 34-92 WILLIAM J. WYE, Primary 'Examiner US. Cl. X.R,62-119, 332, 333

